This invention relates generally to the field of air purification and vacuum cleaning and more specifically to a machine and process for filterless removal of particles and organisms from ambient air, carpets and furnishings. Cleaning the air we breathe has not been of great concern until the accelleration of the industrial boom of the past half century. Industry and automobiles have introduced volumes of pollutants into the atmosphere causing the need for clean air technology to prevent the pollutants from bothering humanity. Clean air technology has gone through several applications and changes. The history of the development of conditioning air includes the development of the industrial emissions scrubber as well as home air cleaners and conditioners to control temperature, the humidifier or de-humidifier to control humidity, killing live organisms using ultra-violet light and the development of better filters for the collection of airborne particles. Clean air has recently been recognized as an important factor for healthy living and the prevention of diseases such as allergies, asthma, cancer causing radio activity and virus or bacteria related ailments. The pattern of development of home air cleaners has paralleled the development of industrial technologies for emissions control. Emissions scrubbers have been created, using the application of three mainstream technologies for removal of particulates and gases from industrial exhaust. These three mainstream technologies are wet scrubbers, filters and electrostatic precipitation. The need for filterless air cleaning has become more evident with increased public consciousness of the importance of clean air in the home and elsewhere for the prevention of disease and the desire for convenience of cleaning the air and furnishings without the burden of handling the collected pollution laden particles when changing filters, wiping plates, emptying bags etc.
Technology has been developed for the collection of particles from the air by applying the principles of emissions scrubbing introduced for industrial applications. Such technologies and variations thereof include filtered systems, wet systems and electrostatic precipitation such as represented by U.S. Pat. No. 6,503,302, Wang, U.S. Pat. No. 2,221,572, Brock, and U.S. Pat. No. 5,925,171, Pietrobon, respectively. All of such systems require periodical cleaning and/or servicing. Filters have been improved to be effective in collection of particles smaller than 1 micron but the smaller the particles collected, the higher the pressure drop because of flow restrictions caused by finer and finer filters.
A wet cleaning system which is commonly used in industry is the venturi scrubber. The venturi scrubber was originated with the idea of squeezing the fluid and particles together through a high velocity, low pressure narrow neck, as opposed to the wider effect of the fan, to reduce surface tension interference with the mixing process. The venturi method provides substantially improved particle/droplet contacting than the standard wet scrubber when used for mist collection. The contacting is done, however, with the same application and effect as the original fan dust collector in that the particles and droplets are all traveling in the same direction, parallel with one another. Improvements and variations to cause higher effectiveness of venturi scrubbing have been accomplished. U.S. Pat. No. 4,469,49, September 1984, Tuovinen discloses more efficient method for the enhancement of a venturi scrubber. Since mist particles are wetted by pre-moistening they become more readily collected in unidirectional flow because of compatibility with additional fluid surfaces. Accelerating the fluid of the venturi scrubber decreases pressure and surface tension in the fluid which promotes the effect of water/particle absorption. A new variation of the method was introduced in 2001 by Pakkala U.S. Pat. No. 6,228,154 using pods and enhancing the collection of a venturi type system by varying the closure of the throat in the atomizer accompanying a venturi process. Schwab, U.S. Pat. No. 6,383,260, 2002 introduced a means of counterflow within a venturi in an attempt to further enhance venturi collection effectiveness. Both of these methods cause a substantial increase in pressure drop proportional to orifice closure and proportional to the improvement of the collection effectiveness of a venturi scrubber.
Standard wet scrubbers are most often used for dust and large particulate collection. Standard wet scrubbers use either a water bath through which to pass the gases or they may employ some type of droplet particle contacting means within a tank. In the droplet spray application, the droplets are introduced from a nozzle or nozzles at a size of about 40 micron at the top of the scrubber tank and the gases are discharged into the bottom. The droplets and particles are intended to collide within the water curtain and absorb the particles into solution. There have been several variations of particle to droplet contacting of wet scrubbing to improve collection effectiveness. As previously illustrated with other scrubbing methods, wet scrubbing applications have also been applied to vacuum cleaners such as U.S. Pat. No. 6,521,027, Wang, 2003, whereby fluids are scattered and spread to contact airborne particles.
Rotary atomization of fluid droplets will reduce their size to about 10 microns in diameter. It is significant to note that rotary atomization can be made to produce more consistent sized droplets. Varying the speed of the atomizer will effect the size of the droplets. The configuration of the atomizer disk will control the consistency. The rotary atomizer has demonstrated that it is the most effective and efficient method known for droplet size reduction and size control.
Electrostatic precipitation (ESP) is a process where particles are ionically charged at entry with a positive or negative polarity. The passing particles are then attracted to a plate or other device that is oppositely charged where they are collected and denied continuance with the gas stream. Patents such as Dawson U.S. Pat. No. 4,265,643, Loreth U.S. Pat. No. 6,203,600 and Aaltonen U.S. Pat. No. 6,228,148 use ESP for cleaning ambient air. Such applications collect particles on a plate or other electrostatically charged media, where they can be removed and disposed of at a later time.
An effective way to apply an air filtering application is represented by U.S. Pat. No. 6,425,932, Huechn, Daros and Bourque, issued in 2002. Filters are effective collectors of microscopic particles but they restrict airflow, especially as they become laden with collected particles. Collecting particles in a filter or a plate retains the particles in accessibility to the living environment until the filter is disposed of or the plate is cleaned and the particles disposed of. Particles that are collected by an air cleaning device should be completely removed from a living atmosphere instead of collecting them into a concentrated accumulation in a filter or a plate. A more desirable and efficient means of removing harmful particles from the air in occupied spaces is naturally a system that removes the particles simultaneously with their collection. Filterless technology can continuously remove particles without reducing airflow.
The development of particle wetting and transfer technology attained a practical limit at 40 micron droplet water nozzle applications in the late 20th century for several reasons, three of which are:    1. The energy requirements to further reduce droplet sizes is costly so efficient methods of droplet size reduction had not been satisfactorily established. 2. Individual demands for better and finer particle size collection was not prominent or did not exist, and 3. Mist collection of super fine, low solubility particles was been difficult because of surface tension and ineffective droplet re-entrainment problems.
A type of mechanical dust collector originated with the injection of water into the intake of a standard air blower with a limited amount of success. Standard blowers have been designed to accomplish the smooth transfer of air without turbulence. Pumps are designed in the same manner and with the same end in mind, that is the smooth, efficient transfer of fluid with the least amount of resistance. The application of such a design for scrubbing will produce, at best, an accidental surface contact or collision of particles with droplets since the particles and droplets are traveling smoothly (by purpose of the design) along the same paths and in the same direction with one another and through wider and wider passages through the blower chamber. This type of scrubber, although having a degree of effectiveness for dust collection has proven inefficient for the collection of gases and therefore has no application. Collisions occurring in the early conventional wet scrubbing system environment have proven to be somewhat inefficient because of the natural dodging action of the particles and droplets from one another. This process also shows insufficient temperature drop for condensing and re-entrainment of solution.
Conventional wet scrubbers show limited efficiency for sulfur dioxide reduction and little effect in the reduction of submicron particle emissions. One reason for the limited collection effect of conventional wet scrubber systems is the interfacial tension of large droplets. The collection of particles is limited and dependent upon contacting on the surface of the droplets. There is also the problem of back mixing. Back mixing is caused by the less than perfect distribution of droplets, large droplets falling faster than small ones and the spray also being applied to the walls of the scrubber chamber and baffles. The deposition of the fluid to the walls and baffles of the system wastes the effect of a large percentage of the scrubbing fluid because fluid surface is decreased with reentrainment of the fluid. Back mixing renders a good deal of the scrubbing fluid useless for collection due to interfacial tension of droplets and surface tension of water curtains formed on the walls. Standard wet scrubbers are largely inefficient because of the dodging effect as particles pass unlike particles or droplets within a gas media without colliding because of the air cushion between the particles and droplets.
Water bath systems are also greatly ineffective for the collection of sub-micron particles since the gas bubble containing the particulates and gases pass through the bath without particles within the bubble contacting with water. Another problem of discharging the particles into the atmosphere is also experienced with wet scrubbers since sufficient drop in temperature is not accomplished to condense the droplets into solution and they are lost into the discharged gas stream.
The collection efficiency of the venturi scrubber severely drops off for the collection of particles below 1 micron in size and, even when using a high pressure drop of as much as 40 inches, less than 80% collection efficiency is observed below 0.5 micron. Major limiting factors in the use of venturi systems are high energy costs to achieve efficiencies in the sub-micron range, the large volume of scrubbing fluid required and the accompanying containment and disposal problems associated therewith.
The use of pneumatics has been unattractive for most scrubbing applications because the high pressure drop required to accomplish the processes results in unacceptably high energy costs. These costs are compounded by the necessity of industry to treat high volumes of gases, thereby making the treatment of a necessary flue gas stream cost prohibitive.
Elecrostatic precipation (ESP) has no way of discharging collected particles without periodical cleaning of the collection medium. ESP is shown to be significantly effective in collecting particles larger than 10 micron and fairly effective above 1 micron but additional technology, such as a HEPA filter is required to collect smaller particles. The problems with ESP are similar to wet scrubbing in that the tiny particles have difficulty passing close enough and with enough polarity to collect on the medium due to collisions with other passing particles and the overpowering conveyance of the air carrier. In order to reduce such negative effects, ESP containments have to be larger and larger, making it hard to find room for ESP treatment for occupied spaces to be applied for cleaning air in areas containing more than about 4000 cubic feet Ultraviolet light is commonly applied in air purification applications to kill live airborne organisms. U.S. Pat. No. 6,576,188, Rose demonstrates an application of Ultraviolet light to sterilize surfaces and air. Ultraviolet light methods of air purification kill organisms but do not remove them from the ambient air.